1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing an optical fiber.
2. Description of the Related Art
In general, an optical fiber is manufactured as follows.
FIG. 7 is a schematic view showing the schematic configuration of an optical fiber manufacturing apparatus used in a conventional optical fiber manufacturing method.
In the manufacture of an optical fiber, first, an optical fiber preform 101 having silica-based glass as a main component is placed in a drawing furnace 102, the distal end of the optical fiber preform 101 is heated to high temperature of 2000° C. in an inert gas atmosphere of argon (Ar), helium (He), and the like, and it is drawn to form a bare optical fiber 103.
Then, the bare optical fiber 103 is fed into a cooling tube 104.
Cooling gas, such as helium or nitrogen gas, is supplied to the cooling tube 104. In the cooling tube 104, the bare optical fiber 103 is quenched to a temperature suitable for forming a primary coating layer in the next step.
Then, the bare optical fiber 103 cooled by the cooling tube 104 is coated with a primary coating layer, which is formed of ultraviolet curable resin or the like, by a coating material application device 105 and a UV lamp 106 for forming the primary coating layer.
In addition, the bare optical fiber 103 on which the primary coating layer is provided is coated with a secondary coating layer, which is formed of ultraviolet curable resin or the like, by a coating material application device 107 and a UV lamp 108 for forming the secondary coating layer. As a result, an optical fiber 109 is formed.
In addition, the optical fiber 109 being drawn is spun using a spinning device 110. The direction of the optical fiber 109 is changed to a different direction by a turn pulley 111, and the optical fiber 109 is wound on a winding drum 114 through a drawing capstan 112 and a dancer roll 113.
In recent years, in order to reduce polarization mode dispersion (hereinafter, abbreviated as “PMD”) of an optical fiber in the manufacture of an optical fiber, the spinning device 110 for spinning the optical fiber 109 is provided in the optical fiber manufacturing apparatus described above, so that the bare optical fiber 103 is drawn while spinning a heated and melted portion of the optical fiber preform 101 (lower end of the optical fiber preform 101).
The spin applied to the optical fiber 109, which is being drawn, using the spinning device 110 is transmitted to the heated and melted portion of the optical fiber preform 101.
For this reason, the bare optical fiber 103 is drawn while the heated and melted portion of the optical fiber preform 101 is being spun.
Accordingly, the spin is fixed to the bare optical fiber 103 after the drawing.
Conventionally, when spinning an optical fiber using a spinning device, a spin torque is applied by pressing the optical fiber bidirectionally with a pair of spinning rollers, for example.
In such a spinning device, spinning is performed while controlling the distance between the spinning rollers in order to reduce damage to the coating layer of the optical fiber, and therefore deformation of the coating layer, peeling of the interface between the primary coating layer and glass, and cracking of the primary coating layer that occurs when there is a lot of damage are prevented (for example, refer to Japanese Patent No. 4194976).
In addition, when drawing an optical fiber with a drawing capstan, a drawing capstan which grips an optical fiber with a capstan wheel and a capstan belt is generally used (for example, refer to Japanese Unexamined Patent Application, First Publication No. H9-227171).
This prevents slippage of the capstan and the optical fiber.
However, in some gripping conditions, the coating layer is damaged, and therefore deformation of the coating layer, peeling of the interface between the primary coating layer and glass, and cracking of the primary coating layer occur.
For this reason, gripping pressure, tensile strength, surface roughness, and a step difference are adjusted to the optimal range in order to reduce damage to the optical fiber coating layer.
Moreover, according to a recent increase in the drawing speed of an optical fiber, improvements in the characteristics of a UV resin material itself (such as improvements in the curing rate) or improvements in optical fiber drawing technology have been made.
However, when increasing the speed by remodeling the conventional device, it is necessary to efficiently dispose a cooling zone, a coating zone, a UV curing zone, a spinning device zone, a drawing capstan zone, and the like in a limited space due to the height restrictions of drawing equipment.
For this reason, a case where the spinning device zone should be set immediately below the UV curing zone or a case where the distance between the UV curing zone and the drawing capstan cannot be sufficiently secured occurs.
As a result, the temperature of the coating layer of the optical fiber at the installation position of the spinning device or the position of the drawing capstan becomes high.
Accordingly, the Young's modulus of the coating layer is reduced, and deformation of the coating layer occurs more easily than before.
As a result, deformation of the optical fiber coat increases even in the range of pressure of a conventional spinning device or pressing force of a drawing capstan belt. Depending on the case, this causes a problem of peeling of the interface between the primary coating layer and glass or cracking of the primary coating layer.
Moreover, in order to introduce a cooler to lower the temperature of the coating layer, it is necessary to secure a new space.
As a result, the balance of the required lengths of various devices (a cooler, a coating device, a UV curing device, and the like) is broken due to height restriction of drawing equipment, making it impossible to increase the drawing speed.
The present invention has been devised in view of such a conventional situation, and it is a first object of the present invention to provide an optical fiber manufacturing method capable of efficiently manufacturing an optical fiber with a high level of reliability by preventing deformation or peeling of a coating layer without reducing the drawing speed.
In addition, it is a second object of the present invention to provide an optical fiber manufacturing apparatus capable of manufacturing an optical fiber with a high level of reliability efficiently by preventing deformation or peeling of a coating layer without complicating the apparatus or reducing the drawing speed.